Warming up to In-Row Cooling

Cooling a Datacenter optimally is the hot topic in the industry, pun unintended. The challenge lies in cooling the datacenter without affecting the operating temperatures of the contained equipment. After going through various approaches like perimeter cooling and using general air conditioners, data centers have now adopted the in-row cooling technique.

Generally, the Computer Room Air Conditioner (CRAC) is built to cool the air within a building. But this approach has its limits. It works wonderfully for a small premise. But when it comes to an entire building, the CRAC has to fight against gravity to replace warm air with cold air. Imagine, having to lift many square feet of cold air to replace with hot air. That takes a lot of electric power, not to mention the additional risk of the mixing of cold air and hot air, which defeats the purpose of cooling.

What is In-Row Cooling?

In perimeter cooling or room-based cooling, there are cooling devices installed around the perimeter of the premise and the servers are placed in the rows in such a way that the backs face each other and the front of the server faced each other to avoid mixing of cold air and hot air. However, this works more effectively in smaller rooms. Bigger the room, harder it is to maintain low temperature.

That’s when a new approach enters the scenario: Room-Based Cooling or In-Row Cooling. The in-row cooling technique is designed to target its cooling towards the server cabinets that fill the data center. This way neither the cool air or the hot air needs to travel much and don’t get a chance to mix. This makes it easy for the equipment to dissipate the heat loads effectively. Using an inrow cooling unit is also much more scalable approach to datacenter cooling; it can be applied each time there is a new cabinet in the datacenter.

Types of In-Row Cooling

There are two types of in-row cooling techniques that can be used in a datacenter:
  • Floor Mount: The air conditioner units work with the same logic as a perimeter cooling, except in a smaller capacity. The units are installed in the rows of the cabinets, supporting a hot aisle/cold aisle arrangement for better air flow and cooling.
  • Overhead: As opposed to the floor mount cooling techniques, this approach is unique in the fact that the cooling units are installed above the server equipment in each rack. What makes this approach advantageous is that it leaves more space for equipment (storage, switches, servers). This technique of overhead in-row cooling is more scalable than floor mount cooling.

Even if the overhead cooling technique leaves more space for equipment, it carries more risk of hot air and cold air mixing. That’s where the floor mount cooling technique comes into picture, as it avoids air mixing.

Irrespective of the type of in-row cooling used, the medium used for cooling the server cabinets is either chilled water or refrigerant.

The main advantage of the in-row cooling is that the airflow is more well-defined than that of the room-based cooling, and therefore, there is more predictability in the airflow paths. As a result, it is possible to utilize the capacity of the air conditioner optimally and achieve high power density. But that is not the only benefit of row-based cooling, there are many other benefits:
  • As mentioned before, the row based cooling is more advantageous because it has smaller air paths and a more channelized cooling technique. This increases the efficiency of the CRAC unit. It is a significant benefit considering that even in smaller datacenters, there have been major losses only because of CRAC unit.
  • Row-based cooling offers a lot of flexibility in adjusting the cooling capacity for each row of equipment. For example, it is possible to have a high cooling in one row for high density applications, and low cooling for other applications. Additionally, it is possible to add redundancy of cooling targeted at specific areas.
  • Unlike a room-based cooling which essentially needs a raised floor architecture, in-row cooling isn’t bound by such architectural restrictions. This results in increase in floor load bearing capacity, and reduced installation costs. As a result, the buildings which don’t have enough headroom for raised floor structure, can easily accommodate the in-row cooling techniques.
In-row cooling technique can be a great success if the right arrangement and layout is applied to the cabinets. That makes it easy for manufacturers to standardize the designs of the rows, to make them immune to the room geometry. Then it shouldn’t matter how the room is shaped and where it is located.

While this technology is very effective, it can be made even more efficient when coupled with the other cooling techniques such as room- and rack- based cooling techniques. 

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